A primary school teacher in York has been charged with more than 20 offences involving children.
Parents of children at three schools where he worked have been sent a letter making them aware of the allegations.
A 31-year-old man appeared before York Magistrates' Court on Friday.
He has been charged with 23 offences, including possessing indecent images, voyeurism, making indecent images, sexual touching and sexual activity with a boy under 13, police said.
In a letter from Eoin Rush, assistant director of York Council, parents were told: "North Yorkshire Police have confirmed that if any parent has not already been contacted by them, it is reasonable to assume that their child has not been affected by this man's alleged behaviour.
"However, it is right to point out that Police enquiries are ongoing and if as a result of these enquiries any further concerns are uncovered the Police will be in contact with anyone affected directly."
A police spokesman said the teacher was granted conditional court bail to an address outside the county.
He is due back at York Magistrates' Court for a committal hearing on 9 May.